We're wrapping up our series looking at the most indispensable players on each Big Ten team. Once again, this is not necessarily a listing of the best players on each team, but ones whose absence would be toughest to absorb because of their particular value or a lack of depth behind them.

We're selecting two players from each Big Ten squad, usually one on offense and one on defense, but not always. In case you missed the previous posts, they're all right here.

Campbell is just a third-year sophomore, but he's the graybeard in Northwestern's secondary, which loses three starters from 2011, including All-Big Ten safety Brian Peters. The Wildcats' struggles against the pass are well documented, and while there's excitement about younger players like cornerback Nick VanHoose, Campbell's experience and leadership is crucial entering the fall. Campbell led the team with 100 tackles, and recorded two interceptions, a fumble recovery, four pass breakups and 3.5 tackles for loss. Although he made his share of mistakes during his redshirt freshman season, he showed good potential and is a favorite among the coaches. Northwestern placed a premium on improved communication this spring after enduring several breakdowns last season. Campbell will be instrumental in this area, and Northwestern simply can't afford to lose him with so much new blood in the secondary.

There's some debate among Northwestern fans about whether Colter should be the starting quarterback, given the concerns about his arm strength. But there's no debate that Colter is the team's best athlete, and a truly dynamic playmaker with the ball in his hands. He showed it last fall when thrust into the starting role for the rehabbing Dan Persa, recording 654 rush yards, 673 pass yards, 466 receiving yards and 18 touchdowns (9 rushing, 6 passing, 3 receiving). Colter led Northwestern to its signature win at Nebraska, and finished the season as one of the nation's most versatile players. If he can complement his top-end running skills with better passing, Northwestern could have one of the Big Ten's most productive offenses yet again. Colter's mobility stands out on a team that hasn't produced an elite running back since 2008 (Tyrell Sutton). Although the team has other options at quarterback, Colter's presence on the field is vital for Northwestern to maintain its success on offense.